A semiconductor wafer is formed to be about 775 μm thick when it is of a 300 mm diameter type in order to avoid its deformation during the previous process. However, this thickness as is, is not suitable for the recent semiconductor packages that are demanded to be thin, so that the wafer is thinned to 100 μm or lower during the process of grinding the rear side called a backgrinding process, then is separated into individual chips by a dicing process.
In the backgrinding process of a semiconductor wafer W, in order to protect the pattern-forming surface of semiconductor wafer W on which circuits have been formed, a soft protection sheet (also called a BG sheet) 1 is adhered to the surface and cut so that its size is marginally greater than the size of semiconductor wafer W (see FIG. 25). Then, semiconductor wafer W is set on the table of a backgrinding machine, and the table is turned so that semiconductor wafer W is placed and positioned in the work area of the grinding machine.
Protection sheet 1 is formed of a lamination of a film base of 50 to 200 μm thick, made of ethylene-vinyl acetate copolymer or soft polyvinyl chloride, and a ultra violet (UV) curable type or non-UV-curing type adhesive layer of 10 to 60 μm thick, of acrylic, urethane, butadiene, silicone or other material, and is peeled off after the backgrinding process and discarded without being reused after once it is used.
After semiconductor wafer W has been placed and positioned in the work area of the grinding machine, the rear side of semiconductor wafer W is ground by a rotary grindstone 33 (see FIG. 26). Then the rear side of semiconductor wafer W is etched about 1 μm by chemical 41 to remove the damaged layer from grinding (see FIG. 27) to thereby achieve the thinning of semiconductor wafer W (see patent document 1).
The semiconductor wafer W, after it has been thus thinned, is fixed to a hollow carrier jig 44 by applying its etched rear side to an adhesive tape, specifically, UV tape 42 that will be used at the dicing process while protection sheet 1 is peeled off from the pattern forming surface of semiconductor wafer W by use of a peeling tape 43 (see FIG. 28), then the semiconductor wafer W supported by carrier jig 44 (see FIG. 29) is divided into individual chips by a grindstone called a blade.    Patent Document 1: Japanese Patent Application Laid-open 2005-93882.